The present embodiment relates generally to a suspending agent for drilling fluids.
While drilling oil and gas wells, a drilling fluid, which may be oil-based or water-based as explained below, is circulated through a drill bit in a well bore and then back to the earth surface, thereby lubricating the drill string and removing cuttings from the well bore. In general, the viscosity of the drilling fluid should be relatively low, while the yield point must be high enough to carry the cuttings out of the hole.
Down hole, the drilling fluid is subjected to relatively high temperatures and relatively high shear rates, which keeps the drilling fluid components in solution. However, drilling fluids are non-Newtonian fluids, in that the viscosity is not constant at all shear rates. Thus, a “freshly built” drilling fluid typically does not have a yield point at a low shear rate sufficient to suspend all of the drilling fluid components, particularly weighting agents. Settling of the components out of solution is a concern for several reasons. For example, after settling, the resulting drilling fluid may not conform to the desired characteristics for a specific drilling application. Likewise, settling can increase transportation costs, due to increased costs for cleaning transport vessels.
Thus, a suspending agent is needed for supporting components in drilling fluids, for example, freshly built drilling fluids. As the drilling fluid will experience higher shear rates once down hole, a suspending agent will not be required permanently. Moreover, a permanently effective suspending agent may cause excessive pump pressure by increasing the viscosity beyond optimal conditions. Therefore, it would be beneficial if the effect of the suspending agent were temporary.